Keyboard keypress issues in Windows 7

I made a rythm game that needs a very fast and accurate response from the keyboard. This game has no problems when i run it in windows XP, but it goes berserk when run in windows 7. Some people also reported this occurence in windows vista.
The main problem is that the timing is not accurate, if one hits the keys perfectly they will just register like 0.2 seconds later which is too late for what I need.
The strange thing is that I could play this for 2 months with windows 7 but now I can’t anymore. maybe I installed something that screwed it up.
They way I’m handling the time of a keypress is by using the getTimer(), but I double it would be any different if I used a new Date().
Is this a known issue? Does anyone know a way to fix this somehow?